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DS2438(3)                    One-Wire File System                    DS2438(3)


DS2438 - Smart Battery Monitor


Temperature Voltages and Current. 26 [.]XXXXXXXXXXXX[XX][/[ CA | EE | date | disconnect/date | disconnect/udate | endcharge/date | endcharge/udate | IAD | offset | pages/page.[0-7|ALL] | temperature | udate | VAD | VDD | vis | See the file man3/standard_mini.3so. ]] Humidity sensor 26 [.]XXXXXXXXXXXX[XX][/[ HIH4000/humidity | HTM1735/humidity | DATANAB/reset | DATANAB/humidity | humidity | temperature ]] Barometer 26 [.]XXXXXXXXXXXX[XX][/[ B1-R1-A/pressure | B1-R1-A/gain | B1-R1-A/offset | ]] Light 26 [.]XXXXXXXXXXXX[XX][/[ S3-R1-A/current | S3-R1-A/illuminance | S3-R1-A/gain ]]




pages/page.0 ... pages/page.7 pages/page.ALL read-write, binary Memory is split into 8 pages of 8 bytes each. Only the pages 3-7 are really available, and some of that appears to be reserved. See the datasheet for details. ALL is an aggregate of the pages. Each page is accessed sequentially. temperature read-only, floating point Temperature read by the chip at high resolution (~13 bits). Units are selected from the invoking command line. See owfs(1) or owhttpd(1) for choices. Default is Celsius. Conversion takes ~20 msec. VAD VDD read-only, floating point Voltage read (~10 bits) at the one of the chip's two supply voltages. Range VDD= 2.4V to 10V, VAD=1.5 to 10V. vis read-only, floating point Current sensor reading, as a voltage difference. Value is in volts. Actual current depends on Rsens resistor (see datasheet). The formula for current is I = vis / Rsens with units in Amps and Ohms. Current measurement will be temporarily enabled (see Ienable ) if not currently enabled (pun intended) for this reading.


CA read-write, yes-no Current Accumulator Configuration flag bit. If "on" (1) current is stored in page 7 bytes 4-7. If "off" (0) that page can be used for general storage. See the datasheet for more information. EE read-write, yes-no Current Accumulator Shadow flag bit. If "on" (1) current reading is stored to EEPROM. If "off" (0) that data will be lost when chip loses power. See the datasheet for more information IAD read-write, yes-no Current A/D Control flag bit. If "on" (1) current measured at 36.41 Hz. If "off" (0) current measurements won't be made. See the datasheet for more information.


date read-write, ascii 26 character date representation of the counter value. Increments once per second. Setting date to a null string will put the current system time. Accepted date formats are: Sat[urday] March 12 12:23:59 2001 Apr[il] 4 9:34:56 2002 3/23/04 23:34:57 current locale setting (your system's format) disconnect/date read-write, ascii 26 character date representation of the disconnect/udate value. Time when the battery pack waws removed from the charger. Format is the same as the date property. disconnect/udate read-write, unsigned integer Representation of disconnect/date as a number. See udate for details. endcharge/date read-write, ascii 26 character date representation of the endcharge/udate value. Format is the same as the date property. endcharge/udate read-write, unsigned integer Representation of endcharge/date as a number. See udate for details. udate read-write, unsigned integer Time represented as a number. udate increments once per second. Usually set to unix time standard: number of seconds since Jan 1, 1970. The date field will be the unix representation (ascii text) of udate and setting either will change the other.


HIH4000/humidity read-only, floating point Relative humidity, as percent (1-100 scale). This value is for a design based on Honeywell's HIH-4000 humidity sensor. HTM1735/humidity read-only, floating point Relative humidity, as percent (1-100 scale). This value is for a design based on Humirel's HTM-1735 humidity sensor. DATANAB/humidity read-only, floating point Based on DataNAB's humidity sensor. It uses a HIH-4000 sensor and the current sensning rather than voltage readings from the DS2438. Calibration values are stored on chip, and a check field is stored in chip memory. DATANAB/reset write-only, yes-no Used to read calibration values and set the chip to current reading more. Should be automatically called when a humidity reading is requested. humidity read-only, floating point Relative humidity, as percent (1-100 scale). The DS2438 actually does not read humidity, but a widely available and publicised circuit based on the chip, does. This design is for the common Honeywell HIH-3610 humidity chip. The mostly compatible HIH-4000 chip uses different temperature compensation, so is better read from the HIH4000/humidity value. See the datasheets for details. If the chip is instead a DATANAB design, the DATANAB/humidity value will be automatically used.


B1-R1-A/pressure read-only, floating point Pressure reading, as milli-bars, or other unit depending on settings/units/pressure_scale. This value is for the B1-R1-A barometer from Hobby-Boards, and assumes the standard calibration. B1-R1-A/gain read/write, floating point Calibration of pressure gain, as signed number, expressed as the same units as B1-R1-A/pressure per volt. This value will be multiplied with the measured voltage to get the B1-R1-A/pressure reading. It may have to be fine tuned for calibration purposes, although with the standard sensor, it will often be good enough to keep it as is. B1-R1-A/offset read/write, floating point Calibration of pressure offset, as signed number, same units as B1-R1-A/pressure. This value will be added to the B1-R1-A/pressure reading. The default value is 904.7 millibars, which may be altered to to compensate for elevation.


S3-R1-A/current read-only, floating point Photo-diode current, in micro-amperes. This value is for the S3-R1-A solar radiation sensor from Hobby-Boards. Due to noise and offsets, this value may read as a negative number in low light conditions. The offset register can be modified to reduce the offset as much as possible. S3-R1-A/illumination read-only, floating point Illumination, in lux. Always a positive number. This value is the lux reading from the solar sensor, taking S3-R1-A/gain into consideration. S3-R1-A/gain read/write, floating point Calibration of photo-diode gain expressed as lux per micro-amperes. The default value is for the SFH203P photo-diode from Osram, used bare. A different gain may be used for instance to compensate for an integrathing, white sphere placed over the diode. This value is for the S3-R1-A solar radiation sensor from Hobby-Boards, using the SFH203P photo-diode from Osram.


MultiSensor/type read-only, ascii For iButtonLink's MultiSensor line of 1-wire devices, give the specific configuration based on a data byte set in memory. (Byte 0 of page 3). This can help interpretation of the sensor values, distinguishing, current from water from light. offset read-write, integer Correction for current readings. A value between -256 and 255. See the datasheet for details. Should be set to the negative of a true zero current reading.


See the file man3/standard.3so.




See the file man3/description.3so. DS2438 The DS2438 (3) is a more complete form of the DS2436 battery chip. Current sensing is available, but not implemented. The major advantage compared to the DS2436 is that two voltages can be read, allowing one to correct circuit measurements for supply voltage and temperature. A better comparison is the DS276x family of chips.


See the file man3/addressing.3so.


http://pdfserv.maxim-ic.com/en/ds/DS2438.pdf http://pdfserv.maxim-ic.com/en/an/humsensor.pdf http://goo.gl/o9DH0 (Redirects to 009012_2.pdf PDF file on honeywell.com website) http://www.phanderson.com/hih-4000.pdf http://www.humirel.com/product/fichier/HTM1735%20RevG%20.pdf


See the file man3/seealso.3so.




Paul Alfille (paul.alfille@gmail.com) Egil Kvaleberg OWFS Manpage 2003 DS2438(3)

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